Recently, various radio communication systems that operate in accordance with 3GPP (Third Generation Partnership Project) protocols are used. In a radio communication system that operates in accordance with LTE/SAE (Long Term Evolution/System Architecture Evolution) protocol in the 3GPP protocols, multiple base stations can cooperate so as to perform radio communication with a user device. The above base stations include, for example, a large-scale radio base station (a macro base station), which has a large communicable region, and a small-scale radio base station (a pico base station, a femto base station, etc.), which has a smaller communicable region than a large-scale radio base station.
As an example of multiple base stations working in cooperation, Patent Document 1 discloses that by multiple femto base stations being grouped based on a geographical criterion (geographical closeness), a handover can be performed between a macro base station and the grouped femto base stations.